No causal connection proved, but study authors suspect one

Action Points

Note that this cross-sectional study using NHANES data suggested that higher levels of certain phthalate and bisphenol chemicals in the urine were associated with varying levels of Vitamin D.

Be aware that the differences in Vitamin D measured were relatively small when compared with the differences seen across races and ethnicities and during different seasons.

Endocrine-disrupting chemicals, including phthalates and BPA, were correlated with decreased circulating levels of vitamin D in adults, researchers said.

The study examined the concentrations of di(2-ethylhexyl) phthalate (DEHP) and bisphenol A (BPA) in urine, and their associations with levels of 25-hydroxyvitamin D [25(OH)D], which could support an adverse effect of exposure to these chemicals, reported Lauren E. Johns, a doctoral candidate in the University of Michigan School of Public Health in Ann Arbor, and colleagues.

Similarly, BPA exposure also had an inverse correlation on circulating vitamin D levels, yet this relationship was observed only among women (-3.71%; 95% CI -6.41 to -1.02; P=0.01), not men (0.88; 95% CI -3.01 to 0.37; P=0.35), the researchers reported in the Journal of Clinical Endocrinology & Metabolism.

Johns and colleagues pointed to data suggesting a negative influence of certain pesticides and pollutants on levels of vitamin D in humans. Because past research suggests low vitamin D levels are associated with a myriad of adverse health outcomes, including chronic kidney disease, birth complications, asthma, diabetes, and more, the authors wanted to look at relationships between phthalate and BPA exposure and vitamin D levels.

"Nearly every person on the planet is exposed to BPA and another class of endocrine-disrupting chemicals called phthalates, so the possibility that these chemicals may even slightly reduce vitamin D levels has widespread implications for public health," stated Johns in a press release. "Vitamin D plays a broad role in maintaining bone and muscle health. In addition, low vitamin D levels have been implicated in outcomes of numerous conditions such as cardiovascular disease, diabetes and cancer."

They drew on data from 2005-2010 in the ongoing National Health and Nutrition Examination Survey, including phthalate metabolites, BPA, creatinine, and serum 25(OH)D, collected from 4,724 adults.

While the authors conclude their research findings are generally consistent with past literature, they emphasize the various confounding variables, such as gender, race/ethnicity, time of year, and consumption of dietary supplements, may have played a big role in the relationships displayed.

"Mean total 25(OH)D concentrations were significantly higher in females than in males, in participants sampled in summer months compared to winter months, and in those who reported taking dietary supplements in the past month that contained vitamin D," reported Johns and colleagues. "All racial/ethnic subgroups had significantly lower total 25(OH)D compared to non-Hispanic whites (mean = 71.8 nmol/L), with the lower mean concentration reported among non-Hispanic blacks (mean = 43.4 nmol/L)."

And they acknowledged that the study design could not support any conclusions about causality. Other potential limits to the study included method of sampling, with the researchers noting that blood samples might be more reliable than urine samples.

"More research is needed into why an association exists, but it is possible that endocrine-disrupting chemicals alter the active form of vitamin D in the body through some of the same mechanisms that they use to impact similar reproductive and thyroid hormones," said John D. Meeker, ScD, senior author of the study, in a press release. "Confirmatory studies are needed to show whether this association exists in other populations."

The study was funded by the Intramural Research Program of the National Institutes of Health, National Institute of Environmental Health Sciences, and National Institutes of Health.

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